Method of applying a spherical correction to map data for rendering direction-of-travel paths on a wireless communications device

ABSTRACT

Displaying a map on a wireless communications device includes steps of obtaining map data for rendering the map to be displayed on the wireless communications device, determining a rotation that, when applied to the map, will orient a selected path in a selected direction, such as a current direction of travel, generating a corrected rotation by applying a spherical correction factor, e.g. based on a current location, and rendering the map on a display of the wireless communications device by applying the corrected rotation. The spherical correction factor corrects for map distortions that occur at high latitudes for paths that are neither purely north-south or east-west. When such a path is rotated to face upward to show direction of travel, the path needs to be straightened by applying the spherical correction factor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/626,605 which claims priority from U.S. Provisional PatentApplication No. 60/788,434 entitled “Methods and Apparatus forDynamically Labelling Map Objects in Visually Displayed Maps of MobileCommunication Devices” filed on Mar. 31, 2006 and from U.S. ProvisionalPatent Application No. 60/787,541 entitled “Method and System forDistribution of Map Content to Mobile Communication Devices” filed onMar. 31, 2006.

TECHNICAL FIELD

The present disclosure relates generally to wireless communicationsdevices and, in particular, to techniques for generating map content onwireless communications devices.

BACKGROUND

Wireless communications devices such as the BlackBerry® by Research inMotion Limited enable users to download map content from web-based datasources such as BlackBerry Maps™, Google Maps™ or Mapquest™. Downloadedmap content is displayed on a small LCD display screen of the wirelesscommunications device for viewing by the user. The user can pan up anddown and side to side as well as zoom in or out. Due to the smalldisplay on the device and due to the limited over-the-air (OTA)bandwidth, there is a need to optimize the delivery and handling of themap data.

Constructing a map projection requires one to fit a curved surface ontoa flat display which necessitates distorting the true layout of theEarth's surface. For example, an equirectangular projection, which is acylindrical map projection, exaggerates the true characteristics of theEarth's surface close to the poles. In other words, the farther from theequator, the more that the equirectangular projection distorts the truesize and proportion of features of the Earth's surface. Thus, forexample, while east-west roads are not distorted, those with both anorth-south and an east-west component appear slanted. Thus, in thenortherly (or southerly) latitudes, roads that are in fact perpendicularappear to intersect at an angle.

With GPS-enabled or other “location-aware” wireless devices, if the mapis rotated to show the direction of travel of the device, i.e. a “trackup” orientation, then the path representing the current direction oftravel path is rendered onscreen at a slight angle.

Although complex algorithms can be devised to compensate for thisdistortion phenomenon, the limited over-the-air (OTA) bandwidth andonboard processing capacity make these complex algorithms generallyunsuitable for use on wireless communications devices. For example,Mercator projections require computationally intensive mathematicsinvolving natural logarithms.

Accordingly, a technique for efficiently compensating for map projectiondistortions on wireless communications devices, particularly in thecontext of devices capable of showing the current direction of travel,remains highly desirable.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present technology will becomeapparent from the following detailed description, taken in combinationwith the appended drawings, in which:

FIG. 1 is a block diagram schematically illustrating pertinentcomponents of a wireless communications device and of a wirelesscommunications network;

FIG. 2 is a more detailed block diagram of a wireless communicationsdevice;

FIG. 3A is a system diagram of exemplary network components whichprovide mapping functionality in the wireless communications devices ofFIG. 1 and FIG. 2;

FIG. 3B illustrates, by way of example only, a message exchange betweena wireless communications device and a map server for downloading mapcontent to the wireless communications device based on the system ofFIG. 3A;

FIG. 3C is a diagram showing a preferred Maplet data structure;

FIG. 4 is a schematic depiction of another example of a wireless networkhaving an applications gateway for optimizing the downloading of mapdata from map servers to wireless communications devices;

FIG. 5 is a flowchart presenting steps of a method of displaying a mapon a wireless device by applying a spherical correction factor tocorrect for distortions in a path representing a current direction oftravel;

FIG. 6A is a depiction of a map of a path which has not yet been rotatedinto a “track up” orientation;

FIG. 6B is a depiction of the map after rotation into the “track up”orientation without the spherical correction;

FIG. 6C is a depiction of the map after rotation into the “track up”orientation with the spherical correction;

FIG. 7A is a screenshot of a map of a path which has not yet beenrotated into a “track up” orientation;

FIG. 7B is a screenshot of the map after rotation into the “track up”orientation without spherical correction; and

FIG. 7C is a screenshot of the map after rotation into the “track up”orientation with the spherical correction.

It will be noted that throughout the appended drawings, like featuresare identified by like reference numerals.

DETAILED DESCRIPTION

The present technology provides, in general, a method for efficientlydisplaying a map on a display screen of a wireless communications devicethat corrects for distortions that occur on cylindrical projection mapsat high northerly (or southerly) latitudes. The distortions arecorrected by applying a spherical correction factor that is thearctangent of the quotient of the tangent of the rotation angle dividedby the cosine of the latitude.

Thus, an aspect of the present technology is a method of displaying amap on a wireless communications device that includes steps of obtainingmap data for rendering the map to be displayed on the wirelesscommunications device, determining a rotation that, when applied to theobtained map data, will orient a selected path of the map in a selecteddirection, generating a corrected rotation by applying a sphericalcorrection factor to the rotation, and rendering a rotated map on adisplay of the wireless communications device by applying the correctedrotation to the obtained map data.

Another aspect of the present technology is a computer program productthat includes code adapted to perform the steps of the foregoing methodwhen the computer program product is loaded into memory and executed ona processor of a wireless communications device.

Yet another aspect of the present technology is a wirelesscommunications device for enabling a user of the device to display a mapon the device that includes an input device for enabling the user tocause the device to obtain map data for rendering the map to bedisplayed on the device, a processor for determining a rotation that,when applied to the obtained map data, will orient a selected path ofthe map in a selected direction and for generating a corrected rotationby applying a spherical correction factor to the rotation, and a displayfor displaying a rotated map rendered by applying the corrected rotationto the obtained map data.

The details and particulars of these aspects of the technology will nowbe described below, by way of example, with reference to the attacheddrawings.

FIG. 1 is a block diagram of a communication system 100 which includes awireless communications device 102 (also referred to as a mobilecommunications device) which communications through a wirelesscommunication network 104. For the purposes of the presentspecification, the expression “wireless communications device”encompasses not only a wireless handheld, cell phone or wireless-enabledlaptop but also any mobile communications device or portablecommunications device such as a satellite phone, wireless-enabled PDA orwireless-enabled MP3 player. In other words, for the purposes of thisspecification, “wireless” shall be understood as encompassing not onlystandard cellular or microwave RF technologies, but also any othercommunications technique that conveys data over the air using anelectromagnetic signal.

The wireless communications device 102 preferably includes a visualdisplay 112, e.g. an LCD screen, a keyboard 114 (or keypad), andoptionally one or more auxiliary user interfaces (UI) 116, each of whichis coupled to a controller 106. The controller 106 is also coupled toradio frequency (RF) transceiver circuitry 108 and an antenna 110.Typically, controller 106 is embodied as a central processing unit (CPU)which runs operating system software in a memory device (described laterwith reference to FIG. 2). Controller 106 normally controls the overalloperation of the wireless communications device 102, whereas signalprocessing operations associated with communications functions aretypically performed in the RF transceiver circuitry 108. Controller 106interfaces with the display screen 112 to display received information,stored information, user inputs, and the like. Keyboard/keypad 114,which may be a telephone-type keypad or a full QWERTY keyboard, isnormally provided for entering commands and data.

The wireless communications device 102 sends communication signals toand receives communication signals from network 104 over a wireless linkvia antenna 110. RF transceiver circuitry 108 performs functions similarto those of station 118 and Base Station Controller (BSC) 120,including, for example, modulation and demodulation, encoding anddecoding, and encryption and decryption. It will be apparent to thoseskilled in the art that the RF transceiver circuitry 108 will be adaptedto the particular wireless network or networks in which the wirelesscommunications device is intended to operate.

The wireless communications device 102 includes a battery interface 134for receiving one or more rechargeable batteries 132. Battery 132provides electrical power to electrical circuitry in the device 102, andbattery interface 134 provides for a mechanical and electricalconnection for battery 132. Battery interface 134 is couple to aregulator 136 which regulates power to the device. When the wirelessdevice 102 is fully operationally, an RF transmitter of RF transceivercircuitry 108 is typically keyed or turned on only when it is sending tonetwork, and is otherwise turned off to conserve resources. Similarly,an RF receiver of RF transceiver circuitry 108 is typically periodicallyturned off to conserve power until it is needed to receive signals orinformation (if at all) during designated time periods.

Wireless communications device 102 operates using a Subscriber IdentityModule (SIM) 140 which is connected to or inserted in the wirelesscommunications device 102 at a SIM interface 142. SIM 140 is one type ofa conventional “smart card” used to identify an end user (or subscriber)of wireless device 102 and to personalize the device, among otherthings. By inserting the SIM card 140 into the wireless communicationsdevice 102, an end user can have access to any and all of his subscribedservices. SIM 140 generally includes a processor and memory for storinginformation. Since SIM 140 is coupled to SIM interface 142, it iscoupled to controller 106 through communication lines 144. In order toidentify the subscriber, SIM 140 contains some user parameters such asan International Mobile Subscriber Identity (IMSI). An advantage ofusing SIM 140 is that end users are not necessarily bound by any singlephysical wireless device. SIM 140 may store additional user informationfor the wireless device as well, including datebook (calendar)information and recent call information.

The wireless communications device 102 may consist of a single unit,such as a data communication device, a cellular telephone, a GlobalPositioning System (GPS) unit, a multiple-function communication devicewith data and voice communication capabilities, a wireless-enabledpersonal digital assistant (PDA), or a wireless-enabled laptop computer.Alternatively, the wireless communications device 102 may be amultiple-module unit comprising a plurality of separate components,including but in no way limited to a computer or other device connectedto a wireless modem. In particular, for example, in the block diagram ofFIG. 1, RF circuitry 108 and antenna 110 may be implemented as a radiomodem unit that may be inserted into a port on a laptop computer. Inthis case, the laptop computer would include display 112, keyboard 114,one or more auxiliary UIs 116, and controller 106 embodied as thecomputer's CPU.

The wireless communications device 102 communicates in and through awireless communication network 104. The wireless communication networkmay be a cellular telecommunications network. In the example presentedin FIG. 1, wireless network 104 is configured in accordance with GlobalSystems for Mobile communications (GSM) and General Packet Radio Service(GPRS) technologies. Although wireless communication network 104 isdescribed herein as a GSM/GPRS-type network, any suitable networktechnologies may be utilized such as Code Division Multiple Access(CDMA), Wideband CDMA (WCDMA), whether 2G, 3G, or Universal MobileTelecommunication System (UMTS) based technologies. In this example, theGSM/GPRS wireless network 104 includes a base station controller (BSC)120 with an associated tower station 118, a Mobile Switching Center(MSC) 122, a Home Location Register (HLR) 132, a Serving General PacketRadio Service (GPRS) Support Node (SGSN) 126, and a Gateway GPRS SupportNode (GGSN) 128. MSC 122 is coupled to BSC 120 and to a landlinenetwork, such as a Public Switched Telephone Network (PSTN) 124. SGSN126 is coupled to BSC 120 and to GGSN 128, which is, in turn, coupled toa public or private data network 130 (such as the Internet). HLR 132 iscoupled to MSC 122, SGSN 126 and GGSN 128.

Tower station 118 is a fixed transceiver station. Tower station 118 andBSC 120 may be referred to as transceiver equipment. The transceiverequipment provides wireless network coverage for a particular coveragearea commonly referred to as a “cell”. The transceiver equipmenttransmits communication signals to and receives communication signalsfrom wireless communications devices 102 within its cell via station118. The transceiver equipment normally performs such functions asmodulation and possibly encoding and/or encryption of signals to betransmitted to the wireless communications device in accordance withparticular, usually predetermined, communication protocols andparameters. The transceiver equipment similar demodulates and possiblydecodes and decrypts, if necessary, any communication signals receivedfrom the wireless communications device 102 transmitting within itscell. Communication protocols and parameters may vary between differentnetworks. For example, one network may employ a different modulationscheme and operate at different frequencies than other networks.

The wireless link shown in communication system 100 of FIG. 1 representsone or more different channels, typically different radio frequency (RF)channels, and associated protocols used between wireless network 104 andwireless communications device 102. An RF channel is a limited resourcethat must be conserved, typically due limits in overall bandwidth and alimited battery power of the wireless device 102. Those skilled in theart will appreciate that a wireless network in actual practice mayinclude hundreds of cells, each served by a station 118, depending upondesired overall expanse of network coverage. All pertinent componentsmay be connected by multiple switches and routers (not shown),controlled by multiple network controllers.

For all wireless communications devices 102 registered with a networkoperator, permanent data (such as the user profile associated with eachdevice) as well as temporary data (such as the current location of thedevice) are stored in the HLR 132. In case of a voice call to thewireless device 102, the HLR 132 is queried to determine the currentlocation of the device 102. A Visitor Location Register (VLR) of MSC 122is responsible for a group of location areas and stores the data ofthose wireless devices that are currently in its area of responsibility.This includes parts of the permanent data that have been transmittedfrom HLR 132 to the VLR for faster access. However, the VLR of MSC 122may also assign and store local data, such as temporary identifications.Optionally, the VLR of MSC 122 can be enhanced for more efficientco-ordination of GPRS and non-GPRS services and functionality (e.g.paging for circuit-switched calls which can be performed moreefficiently via SGSN 126, and combined GPRS and non-GPRS locationupdates).

Serving GPRS Support Node (SGSN) 126 is at the same hierarchical levelas MSC 122 and keeps track of the individual locations of wirelessdevices 102. SGSN 126 also performs security functions and accesscontrol. Gateway GPRS Support Node (GGSN) 128 provides internetworkingwith external packet-switched networks and is connected with SGSNs (suchas SGSN 126) via an IP-based GPRS backbone network. SGSN 126 performsauthentication and cipher setting procedures based on the samealgorithms, keys, and criteria as in existing GSM. In conventionaloperation, cell selection may be performed autonomously by wirelessdevice 102 or by the transceiver equipment instructing the wirelessdevice to select a particular cell. The wireless device 102 informswireless network 104 when it reselects another cell or group of cells,known as a routing area.

In order to access GPRS services, the wireless device 102 first makesits presence known to wireless network 104 by performing what is knownas a GPRS “attach”. This operation establishes a logical link betweenthe wireless device 102 and SGSN 126 and makes the wireless device 102available to receive, for example, pages via SGSN, notifications ofincoming GPRS data, or SMS messages over GPRS. In order to send andreceive GPRS data, the wireless device 102 assists in activating thepacket data address that it wants to use. This operation makes thewireless device 102 known to GGSN 128; internetworking with externaldata networks can thereafter commence. User data may be transferredtransparently between the wireless device 102 and the external datanetworks using, for example, encapsulation and tunneling. Data packetsare equipped with GPRS-specific protocol information and transferredbetween wireless device 102 and GGSN 128.

Those skilled in the art will appreciate that a wireless network may beconnected to other systems, possibly including other networks, notexplicitly shown in FIG. 1. A network will normally be transmitting atvery least some sort of paging and system information on an ongoingbasis, even if there is no actual packet data exchanged. Although thenetwork consists of many parts, these parts all work together to resultin certain behaviours at the wireless link.

FIG. 2 is a detailed block diagram of a preferred wirelesscommunications device 202. The wireless device 202 is preferably atwo-way communication device having at least voice and advanced datacommunication capabilities, including the capability to communicate withother computer systems. Depending on the functionality provided by thewireless device 202, it may be referred to as a data messaging device, atwo-way pager, a cellular telephone with data message capabilities, awireless Internet appliance, or a data communications device (with orwithout telephony capabilities). The wireless device 202 may communicatewith any one of a plurality of fixed transceiver stations 200 within itsgeographic coverage area.

The wireless communications device 202 will normally incorporate acommunication subsystem 211, which includes a receiver 212, atransmitter 214, and associated components, such as one or more(preferably embedded or internal) antenna elements 216 and 218, localoscillators (LO's) 213, and a processing module such as a digital signalprocessor (DSP) 220. Communication subsystem 211 is analogous to RFtransceiver circuitry 108 and antenna 110 shown in FIG. 1. As will beapparent to those skilled in the field of communications, the particulardesign of communication subsystem 211 depends on the communicationnetwork in which the wireless device 202 is intended to operate.

The wireless device 202 may send and receive communication signals overthe network after required network registration or activation procedureshave been completed. Signals received by antenna 216 through the networkare input to receiver 212, which may perform common receiver functionsas signal amplification, frequency down conversion, filtering, channelselection, and the like, and, as shown in the example of FIG. 2,analog-to-digital (A/D) conversion. A/D conversion of a received signalallows more complex communication functions such as demodulation anddecoding to performed in the DSP 220. In a similar manner, signals to betransmitted are processed, including modulation and encoding, forexample, by DSP 220. These DSP-processed signals are input totransmitter 214 for digital-to-analog (D/A) conversion, frequency upconversion, filtering, amplification and transmission over communicationnetwork via antenna 218. DSP 220 not only processes communicationsignals, but also provides for receiver and transmitter control. Forexample, the gains applied to communication signals in receiver 212 andtransmitter 214 may be adaptively controlled through automatic gaincontrol algorithms implemented in the DSP 220.

Network access is associated with a subscriber or user of the wirelessdevice 202, and therefore the wireless device requires a SubscriberIdentity Module or SIM card 262 to be inserted in a SIM interface 264 inorder to operate in the network. SIM 262 includes those featuresdescribed in relation to FIG. 1. Wireless device 202 is abattery-powered device so it also includes a battery interface 254 forreceiving one or more rechargeable batteries 256. Such a battery 256provides electrical power to most if not all electrical circuitry in thedevice 102, and battery interface provides for a mechanical andelectrical connection for it. The battery interface 254 is coupled to aregulator (not shown) which provides a regulated voltage V to all of thecircuitry.

Wireless communications device 202 includes a microprocessor 238 (whichis one implementation of controller 106 of FIG. 1) which controlsoverall operation of wireless device 202. Communication functions,including at least data and voice communications, are performed throughcommunication subsystem 211. Microprocessor 238 also interacts withadditional device subsystems such as a display 222, a flash memory 224,a random access memory (RAM) 226, auxiliary input/output (I/O)subsystems 228, a serial port 230, a keyboard 232, a speaker 234, amicrophone 236, a short-range communications subsystem 240, and anyother device subsystems generally designated at 242. Some of thesubsystems shown in FIG. 2 perform communication-related functions,whereas other subsystems may provide “resident” or on-board functions.Notably, some subsystems, such as keyboard 232 and display 222, forexample, may be used for both communication-related functions, such asentering a text message for transmission over a communication network,and device-resident functions such as a calculator or task list.Operating system software used by the microprocessor 238 is preferablystored in a persistent (non-volatile) store such as flash memory 224,which may alternatively be a read-only memory (ROM) or similar storageelement (not shown). Those skilled in the art will appreciate that theoperating system, specific device applications, or parts thereof, may betemporarily loaded into a volatile store such as RAM 226.

Microprocessor 238, in addition to its operating system functions,enables execution of software applications on the wireless device 202. Apredetermined set of applications which control basic device operations,including at least data and voice communication applications, willnormally be installed on the device 202 during its manufacture. Forexample, the device may be pre-loaded with a personal informationmanager (PIM) having the ability to organize and manage data itemsrelating to the user's profile, such as e-mail, calendar events, voicemails, appointments, and task items. Naturally, one or more memorystores are available on the device 202 and SIM 256 to facilitate storageof PIM data items and other information.

The PIM application preferably has the ability to send and receive dataitems via the wireless network. PIM data items may be seamlesslyintegrated, synchronized, and updated via the wireless network, with thewireless device user's corresponding data items stored and/or associatedwith a host computer system thereby creating a mirrored host computer onthe wireless device 202 with respect to such items. This is especiallyadvantageous where the host computer system is the wireless deviceuser's office computer system. Additional applications may also beloaded into the memory store(s) of the wireless communications device202 through the wireless network, the auxiliary I/O subsystem 228, theserial port 230, short-range communications subsystem 240, or any othersuitable subsystem 242, and installed by a user in RAM 226 or preferablya non-volatile store (not shown) for execution by the microprocessor238. Such flexibility in application installation increases thefunctionality of the wireless device 202 and may provide enhancedonboard functions, communication-related functions or both. For example,secure communication applications may enable electronic commercefunctions and other such financial transactions to be performed usingthe wireless device 202.

In a data communication mode, a received signal such as a text message,an e-mail message, or a web page download will be processed bycommunication subsystem 211 and input to microprocessor 238.Microprocessor 238 will preferably further process the signal for outputto display 222 or alternatively to auxiliary I/O device 228. A user ofthe wireless device 202 may also compose data items, such as emailmessages, for example, using keyboard 232 in conjunction with display222 and possibly auxiliary I/O device 228. Keyboard 232 is preferably acomplete alphanumeric keyboard and/or telephone-type keypad. Thesecomposed items may be transmitted over a communication network throughcommunication subsystem 211.

For voice communications, the overall operation of the wirelesscommunications device 202 is substantially similar, except that thereceived signals would be output to speaker 234 and signals fortransmission would be generated by microphone 236. Alternative voice oraudio I/O subsystems, such as a voice message recording subsystem, mayalso be implemented on the wireless device 202. Although voice or audiosignal output is preferably accomplished primarily through speaker 234,display 222 may also be used to provide an indication of the identity ofthe calling party, duration on a voice call, or other voice call relatedinformation, as some examples.

Serial port 230 in FIG. 2 is normally implemented in a personal digitalassistant (PDA)-type communication device for which synchronization witha user's desktop computer is a desirable, albeit optional, component.Serial port 230 enables a user to set preferences through an externaldevice or software application and extends the capabilities of wirelessdevice 202 by providing for information or software downloads to thewireless device 202 other than through the wireless network. Thealternate download path may, for example, be used to load an encryptionkey onto the wireless device 202 through a direct and thus reliable andtrusted connection to thereby provide secure device communications.

Short-range communications subsystem 240 of FIG. 2 is an additionaloptional component which provides for communication between mobilestation 202 and different systems or devices, which need not necessarilybe similar devices. For example, subsystem 240 may include an infrareddevice and associated circuits and components, or a Bluetooth®communication module to provide for communication with similarly-enabledsystems and devices. Bluetooth® is a trademark of Bluetooth SIG, Inc.

FIG. 3A is a system diagram of network components which provide mappingfunctionality in the wireless communication devices of FIGS. 1 and 2. Toachieve this, a mapping application is also provided in memory of thewireless communications device for rendering visual maps in its display.Wireless communications devices 202 are connected over a mobile carriernetwork 303 for communication through a firewall 305 to a relay 307. Arequest for map data from any one of the wireless communications devices202 is received at relay 307 and passed via a secure channel 309 throughfirewall 311 to a corporate enterprise server 313 and corporate mobiledata system (MDS) server 315. The request is then passed via firewall317 to a public map server and/or to a public location-based service(LBS) server 321 which provides location-based services (LBS) to handlethe request. The network may include a plurality of such map serversand/or LBS servers where requests are distributed and processed througha load distributing server. The map/LBS data may be stored on thisnetwork server 321 in a network database 322, or may be stored on aseparate map server and/or LBS server (not shown). Private corporatedata stored on corporate map/LBS server 325 may be added to the publicdata via corporate MDS server 315 on the secure return path to thewireless device 202. Alternatively, where no corporate servers areprovided, the request from the wireless device 202 may be passed viarelay 307 to a public MDS server 327, which sends the request to thepublic map/LBS server 321 providing map data or other local-basedservice in response to the request. For greater clarity, it should beunderstood that the wireless devices can obtain map data from a “pure”map server offering no location-based services, from an LBS serveroffering location-based services in addition to map content, or from acombination of servers offering map content and LBS.

A Maplet data structure is provided that contains all of the graphic andlabelled content associated with a geographic area (e.g. map featuressuch as restaurants (point features), streets (line features) or lakes(polygon features)). Maplets are structured in Layers of Data Entries(“DEntries”) identified by a “Layer ID” to enable data from differentsources to be deployed to the device and meshed for proper rendering.Each DEntry is representative of one or more artefact or label (or acombination of both) and includes coordinate information (also referredto as a “bounding box” or “bounding area”) to identify the area coveredby the DEntry and a plurality of data points that together represent theartefact, feature or label. For example, a DEntry may be used torepresent a street on a city map (or a plurality of streets), whereinthe various points within the DEntry are separated into different partsrepresenting various portions of the artefact or map feature (e.g.portions of the street). A wireless device may issue a request for themap server to download only those DEntries that are included within aspecified area or bounding box representing an area of interest that canbe represented by, for example, a pair of bottom left, top rightcoordinates.

As depicted in FIG. 3B, the wireless communications device issues one ormore AOI (Area of Interest) requests, DEntry or data requests and MapletIndex requests to the map server for selective downloading of map databased on user context. Thus, rather than transmitting the entire mapdata for an area in reply to each request from the device (which burdensthe wireless link), local caching may be used in conjunction withcontext filtering of map data on the server. For example, if a user'swireless device is GPS enabled and the user is traveling in anautomobile at 120 km/h along a freeway then context filtering can byemployed to prevent downloading of map data relating to passing sidestreets. Or, if the user is traveling in an airplane at 30,000 feet,then context filtering can be employed to prevent downloading of mapdata for any streets whatsoever. Also, a user's context can be defined,for example, in terms of occupation, e.g. a user whose occupation is atransport truck driver can employ context filtering to preventdownloading of map data for side streets on which the user's truck isincapable of traveling, or a user whose occupation is to replenishsupplied of soft drink dispensing machines can employ context filteringto download public map data showing the user's geographical area ofresponsibility with irrelevant features such as lakes and parks filteredout and private map data containing the location of soft drinkdispensing machines superimposed on the public map data.

The Maplet Index request results in a Maplet Index (i.e. only a portionof the Maplet that provides a table of contents of the map dataavailable within the Maplet rather than the entire Maplet) beingdownloaded from the map server to the device, thereby conserving OTA(Over-the-Air) bandwidth and device memory caching requirements. TheMaplet Index conforms to the same data structure as a Maplet, but omitsthe data points. Consequently, the Maplet Index is small (e.g. 300-400bytes) relative to the size of a fully populated Maplet or aconventional bit map, and includes DEntry bounding boxes and attributes(size, complexity, etc.) for all artefacts within the Maplet. As thefield of view changes (e.g. for a location-aware device that displays amap while moving), the device (client) software assesses whether or notit needs to download additional data from the server. Thus, if the sizeattribute or complexity attribute of an artefact that has started tomove into the field of view of the device (but is not yet beingdisplayed) is not relevant to the viewer's current context, then thedevice can choose not to display that portion of the artifact. On theother hand, if the portion of the artefact is appropriate for display,then the device accesses its cache to determine whether the DEntriesassociated with that portion of the artefact have already beendownloaded, in which case the cached content is displayed. Otherwise,the device issues a request for the map server to download all the ofthe DEntries associated with the artifact portion.

By organizing the Maplet data structure in Layers, it is possible toseamlessly combine and display information obtained from public andprivate databases. For example, it is possible for the device to displayan office building at a certain address on a street (e.g. a 1st z-orderattribute from public database), adjacent a river (e.g. a 2nd z-orderattribute from public database), with a superimposed floor plan of thebuilding to show individual offices (e.g. 11th z-order attribute from aprivate database, accessible through a firewall).

Referring back to FIG. 3A, within the network having map server(s)and/or LBS server(s) 321 and database(s) 322 accessible to it, all ofthe map data for the entire world is divided and stored as a gridaccording to various levels of resolution (zoom), as set forth below inTable A. Thus, a single A-level Maplet represents a 0.05×0.05 degreegrid area; a single B-level Maplet represents a 0.5×0.5 degree gridarea; a single C-level Maplet represents a 5×5 degree grid area; asingle D-level Maplet represents a 50×50 degree grid area; and a singleE level Maplet represents the entire world in a single Maplet. It isunderstood that Table A is only an example of a particular Maplet griddivision; different grid divisions having finer or coarser granularitymay, of courser, be substituted. A Maplet includes a set of layers, witheach layer containing a set of DEntries, and each DEntry containing aset of data points.

TABLE A # of Maplets # of Maplets # of Maplets Grid to cover to cover tocover Level (degrees) the World North America Europe A 0.05 × 0.0525,920,000 356,000 100,000 B 0.5 × 0.5 259,200 6,500 1000 C 5 × 5 2,59296 10 D 50 × 50 32 5 5 E World 1 1 1

As mentioned above, three specific types of requests may be generated bya wireless communications device (i.e. the client)—AOI requests, DEntryrequests and Maplet Index requests. The requests may be generatedseparately or in various combinations, as discussed in greater detailbelow. An AOI (area of interest) request calls for all DEntries in agiven area (bounding box) for a predetermined or selected set of z-orderLayers. The AOI request is usually generated when the device moves to anew area so as to fetch DEntries for display before the device clientknows what is available in the Maplet. The Maplet Index has the exactsame structure as a Maplet but does not contain complete DEntries (i.e.the data Points actually representing artifacts and labels are omitted).Thus, a Maplet Index defines what Layers and DEntries are available fora given Maplet. A data or DEntry request is a mechanism to bundletogether all of the required Dentries for a given Maplet.

Typically, AOI and Maplet Index requests are paired together in the samemessage, although they need not be, while DEntry requests are generatedmost often. For example, when a wireless device moves into an area forwhich no information has been stored on the device client, the MapletIndex request returns a Maplet Index that indicates what data the clientcan specifically request from the server 321, while the AOI requestreturns any DEntries within the area of interest for the specifiedLayers (if they exist). In the example requests shown on FIG. 3B, thedesired Maplet is identified within a DEntry request by specifying thebottom-left Maplet coordinate. In addition, the DEntry request mayinclude a layer mask so that unwanted Layers are not downloaded, aDEntry mask so that unwanted data Points are not downloaded, and zoomvalues to specify a zoom level for the requested DEntry. Once the deviceclient has received the requested Maplet Index, the client typicallythen issues multiple DEntry requests to ask for specific DEntries (sincethe client knows all of the specific DEntries that are available basedon the Maplet Index).

In this particular implementation, a collection of 20×20 A-level Maplets(representing a 1×1 degree square) is compiled into a Maplet Block File(.mbl). An .mbl file contains a header which specifies the offset andlength of each Maplet in the .mbl file. The same 20×20 collection ofMaplet index data is compiled into a Maplet Index file (.mbx). The .mbland .mbx file structures are set forth in Tables B and C, respectively.

TABLE B Address Offset Offset Length 0 × 000 Maplet #0 Offset Maplet #0Length (4 bytes) (4 bytes) 0 × 008 Maplet #1 Offset Maplet #1 Length 0 ×010 Maplet #2 Offset Maplet #2 Length . . . . . . . . . 0 × C78 Maplet#399 Offset Maplet #399 Length 0 × C80 Beginning of Maplet #0 0 × C80 +Size of Beginning of Maplet #1 Maplet #0 0 × C80 + Size of Beginning ofMaplet #2 Maplet #0 + #1 ... ... 0 × C80 + Σ of Size Beginning of Maplet#399 of Maplets (#0: #398)

In Table B, the offset of Maplet #0 is 0x0000_(—)0000 since, in thisparticular example, the data structure is based on the assumption thatthe base address for the actual Maplet data is 0x0000_(—)0C80. Thereforethe absolute address for Maplet #0 data is: Maplet #0 Address=BaseAddress (0x0000_(—)0C80)+Maplet #0 Offset (0x0000_(—)0000), andadditional Maplet addresses are calculated as: Maplet #(n+1)Offset=Maplet #(n) Offset+Maplet #(n) Length. If a Maplet has no data ordoes not exist, the length parameter is set to zero (0x0000_(—)0000).

TABLE C Address Offset Offset (4 bytes) Length (4 bytes) 0 × 000 MapletIndex #0 Offset Maplet #0 Length 0 × 008 Maplet Index #1 Offset Maplet#1 Length 0 × 010 Maplet Index #2 Offset Maplet #2 Length . . . . . . .. . 0 × C78 Maplet Index #399 Offset Maplet Index #399 Length 0 × C80Beginning of Maplet Index #0 0 × C80 + Size of Beginning of Maplet Index#1 Maplet Index #0 0 × C80 + Size of Beginning of Maplet Index #2 MapletIndex #0 + #1 ... ... 0 × C80 + Σ of Size Beginning of Maplet #399 ofMaplets Indices (#0: #398)

In Table C, the offset of Maplet Index #0 is 0x0000_(—)0000 since,according to an exemplary embodiment the data structure is based on theassumption that the base address for the actual Maplet index data is0x0000_(—)0C80. Therefore, the absolute address for Maplet Index #0 datais: Maplet Index #0 Address=Base Address (0x0000_(—)0C80)+Maplet Index#0 Offset (0x0000_(—)0000), and additional Maplet index addresses arecalculated as: Maplet Index #(n+1) Offset=Maplet Index #(n)Offset+Maplet Index #(n) Length. If a Maplet Index has no data or doesnot exist, the length parameter is set to zero (0x0000_(—)0000).

FIG. 3C and Table D (below), in combination, illustrate, by way ofexample only, a basic Maplet data structure. Generally, as noted above,the Maplet data structure can be said to include a Maplet Index (i.e. anindex of the DEntries, each of which is representative of either anartifact or a label or both) together with data Points for each DEntrythat actually form such artifacts and labels. In this example, eachMaplet includes a Map ID (e.g. 0xA1B1C1D1), the # of Layers in theMaplet, and a Layer Entry for each Layer. The Map ID identifies the dataas a valid Maplet, and according to one alternative, may also be used toidentify a version number for the data. The # of Layers is an integerwhich indicates the number of Layers (and therefore Layer Entries) inthe Maplet. Each Layer Entry defines rendering attributes and isfollowed by a list of DEntries for each Layer. The above forms a MapletIndex. For a complete Maplet, each DEntry contains a set of data Points(referred to herein as oPoints) or Labels). It will be noted that Layerscan have multiple DEntries and the complete list of DEntries and Pointsare grouped by Layer and separated by a Layer Separator (e.g. hex value0xEEEEEEEE). In this example, each Layer Entry is 20 bytes long, and aDEntry is 12 bytes long. However, the number of Layers, number ofDEntries per Layer and the number of Points per DEntry depends on themap data and is generally variable.

Table D provides a high “byte-level” description of a Maplet for thisexample.

TABLE D Data Quantity Total # of Bytes Map ID 1 4 bytes # of Layers 1 4bytes Layer Entries # of Layers 20 bytes × (# of Layers) DEntry of a ×(# of # of Layers 12 bytes × (Σ of the # of Layer DEntries DEntries inof each Layer) + Points for DEntry in a Layer) 4 bytes × (Σ of the # ofPoints of a Layer in each DEntry in each Layer) + Layer Separator 4bytes × (# of Layers)

By way of a further example, the wireless network 200 depicted in FIG. 4can include an applications gateway (AG) 350 for optimizing data flowfor onboard applications such as a mapping application 500 stored inmemory (e.g. stored in a flash memory 224) and executable by themicroprocessor 238 of the wireless device 202.

As shown in FIG. 4, the wireless network 200 hosts a plurality ofhandheld wireless communications devices 202 (such as the BlackBerry® byResearch in Motion Limited) having voice and data capabilities (for bothe-mail and web browsing) as well as a full QWERTY keyboard. Thesewireless communications devices 202 can access Web-based map data onpublic map servers 400 hosted on the Internet or other data network 130via the applications gateway (AG) 350 which mediates and optimizes dataflow between the wireless network 200 and the data network by performingvarious mappings, compressions and optimizations on the data.

The map server extracts generic map content from a GeographicalInformation Systems (GIS) map database (e.g. Navtech®, TelAtlas®, etc.)at a specified level of resolution (zoom level). Custom graphicsassociated with the query, such as highlighted route, pushpin forcurrent position or street address, etc. are post-processed and mergedby the server with the generic map content. Relevant screen graphics arethen labelled, and the merged map graphic is compressed and delivered tothe device for display.

In operation, a user of the wireless communications device 202 uses aninput device such as keyboard 232 and/or thumbwheel/trackball 233 tocause the microprocessor 238 to open the map application 500 stored inthe memory 224. Using the keyboard 232 and thumbwheel/trackball 233, theuser specifies a map location on the map application 500. In response tothis request/command, the microprocessor 238 instructs the RFtransceiver circuitry 211 to transmit the request over the air throughthe wireless network 104. The request is processed by the AG 350 andforwarded into the data network (Internet) using standardpacket-forwarding protocols to one or more of the public and/or privatemap servers 400, 410. Accessing a private map server 410 behind acorporate firewall 420 was described above with reference to FIG. 3A.Map data downloaded from these one or more map servers 400, 410 is thenforwarded in data packets through the data network and mapped/optimizedby the AG 350 for wireless transmission through the wireless network 104to the wireless communications device 202 that originally sent therequest.

The downloaded map data can be cached locally in RAM 226, and displayedon the display 222 or graphical user interface (GUI) of the device aftera corrected rotation is applied to the obtained map data, as will beexplained in greater detail below. If a further request is made by theuser (or if the user wants a change in the field of view by zooming orpanning), the device will check whether the data required can beobtained from the local cache (RAM 226). If not, the device issues a newrequest to the one or more map servers 400, 410 in the same manner asdescribed above.

As described earlier, map data can optionally be downloaded first as aMaplet Index enabling the user to then choose which DEntries listed inthe Index to download in full. Furthermore, as described earlier, themap application can include user-configurable context filtering thatenables the user to filter out unwanted map features or artifacts by notdownloading specific DEntries corresponding to those unwanted mapfeatures or artifacts.

In a preferred implementation, the wireless communications deviceincludes a Global Positioning System (GPS) receiver (“GPS chip”) 550 forproviding location-based services (LBS) to the user in addition to mapcontent. Embedding a GPS chip 550 capable of receiving and processingsignals from GPS satellites enable the GPS chip to generate latitude andlongitude coordinates, thus making the device “location aware”. Toobtain local-based services, the map application within the wirelesscommunications device sends a request to the map server for informationrelating to a city, restaurant, street address, route, etc. If thedevice is “location aware”, the request would include the currentlocation of the device.

In lieu of, or in addition to, GPS coordinates, the location of thedevice can be determined using triangulation of signals from in-rangebase towers, such as used for Wireless E911. Wireless Enhanced 911services enable a cell phone or other wireless device to be locatedgeographically using radiolocation techniques such as (i) angle ofarrival (AOA) which entails locating the caller at the point wheresignals from two towers intersect; (ii) time difference of arrival(TDOA), which uses multilateration like GPS, except that the networksdetermine the time difference and therefore the distance from eachtower; and (iii) location signature, which uses “fingerprinting” tostore and recall patterns (such as multipath) which mobile phone signalsexhibit at different locations in each cell.

Operation of the systems described above will now be described withreference to the method steps depicted in the flowchart of FIG. 5. Asdepicted in FIG. 5, this method of displaying a map on a wirelesscommunications device includes initial steps of opening the mapapplication on the device (step 600) and activating adirection-of-travel mode using the map application (step 602), e.g.specifying that the map should display the current location of thedevice.

At step 604, the device determines its current location. For example, aGPS receiver onboard the device 604 provides GPS coordinates indicativeof the estimated longitude and latitude of the device. Alternatively,triangulation of base station signals can be used.

At step 606, the device obtains map data for the current location. Forthe purposes of this specification, “obtaining map data” means receivingor downloading the map data over the air, i.e. over a wireless link,retrieving the map data from a local cache, or downloading the map dataover a wired connection, or any combination thereof. In other words,obtaining map data includes steps of determining whether the data isalready cached locally. If the data is locally cached, the map data isretrieved from the cache. Otherwise, if not all of the map data iscached, then the map data is downloaded over the air for the currentlocation.

As depicted in FIG. 5, once the map data is obtained, the devicedetermines the rotation (rotation matrix or rotation angle) that isnecessary to orient the current path at a selected direction. In otherwords, step 608 entails determining a rotation that, when applied to theobtained map data, will orient a selected path of the map in a selecteddirection. The map application includes a “track up” mode which orientsthe path corresponding to the current direction of travel in avertically upward orientation. In “track up” mode, therefore, theselected path is the current direction of travel and the selecteddirection is vertically upward.

Once the required rotation is determined, a corrected rotation isgenerated by applying a spherical correction factor to the rotation. Thespherical correction factor is computed (step 610) based on the rotationangle and the current location. In a preferred implementation, thespherical correction factor equals arctangent (tangent(rotationangle)/cosine(latitude)). The computed spherical correction factor isthen applied to generate the rotated map (step 612). As shown in FIG. 5,the rotated map is then rendered on a display of the wirelesscommunications device by applying the corrected rotation to the obtainedmap data.

This spherical correction factor corrects for the map distortions thatinherently occur at northerly or southerly latitudes when cylindricalprojection maps are displayed. This correction is accomplished inreal-time without the need for computationally intensive algorithms thatwould be unsuitable for wireless devices. In other words, since thespherical correction factor is computationally straightforward,real-time distortion-correction can be achieved on a wireless devicewithout unduly burdening wireless bandwidth or onboard processingcapacity.

When computing the spherical correction factor, it is preferable tocalculate a single spherical correction factor for applying to all ofthe vertices of the map to be rendered based on a latitude of a centerof the map.

Preferably, the step of generating the corrected map data entailsincorporating the spherical correction factor into a 2×2 transformationmatrix that transforms (rotates) all vertices in the obtained map data(latitude and longitude coordinates) to rotated and corrected map datato be rendered onto the screen (corrected screen coordinates).Algorithms for performing standard matrix transformations and rotationsare well known in the art. As an example, one matrix transformation thatcan be applied to generate corrected map data (Xcorrected,Ycorrected)would be:

$\left\lbrack \frac{Xcorrected}{Ycorrected} \right\rbrack = {{{\begin{bmatrix}{\cos\;\theta} & {{- \sin}\;\theta} \\{\sin\;\theta} & {\cos\;\theta}\end{bmatrix} \cdot \left\lbrack \frac{X}{Y} \right\rbrack}\mspace{14mu}{where}\mspace{14mu}{SCF}} = {\arctan\left( \frac{\tan\;\theta}{\cos({latitude})} \right)}}$

In this equation, it is implicit that cos(latitude) means the cosine ofthe absolute value of the latitude expressed in degrees (where minutesand seconds are converted into decimals of degrees). The angle theta θrepresents the angle of rotation and X,Y represent coordinates of theobtained map before the corrected rotation is applied.

By way of example, consider the map 700 shown in FIG. 6A. This map showsthe current location 710 of the device as well as the current directionof travel 720 of the device along the path “Main Street” 730. Assume,again for the purposes of illustration, that this current location onMain Street is far from the equator, e.g. in a city that is 40-50degrees North and thus susceptible to the sort of distortions that ariseat northerly latitudes due to the cylindrical (“equirectangular”)projection of the map. In other words, because Main Street is neitherpurely north-south nor is it purely east-west, this path will appear tobe slightly angled from its actual orientation.

As shown in FIG. 6B, when the map is rotated, using conventionalrotation techniques, to attempt to orient the path in the “track up”orientation, i.e. the path points vertically upward on the display, thepath is visibly angled from the vertical (an “almost track up”condition). Main Street is not perfectly vertical due to the distortionsthat arise due to the cylindrical projection of the map at northerly (orsoutherly) latitudes.

By applying the spherical correction factor to the rotation matrix, orto the vector rotation, corrected map data are obtained which rotatesthe direction-of-travel path (Main Street) so that it becomessubstantially vertical as desired. As will be appreciated, the rotationof the direction-of-travel path need not always align this path with thevertical. A setting in the map application may be provided to enable theuser to specify whether the direction-of-travel path should be pointingup (“track up”) or pointing in another direction (e.g. horizontally tothe right).

FIG. 7A is a screenshot of a map of a path (“Columbia Street”) which hasnot yet been rotated into a “track up” orientation. This street isneither purely north-south nor purely east-west, and thus susceptible todistortions at high latitudes. FIG. 7B is a screenshot of the map afterrotation into the “track up” orientation without the sphericalcorrection. Note how Columbia Street is not perfectly vertical, due tothe cylindrical projection distortion arising at high latitude. FIG. 7Cis a screenshot of the map after rotation into the “track up”orientation with the spherical correction. Note how Columbia Street nowpoints vertically upwards, as it should when the map application is inthe “track up” mode.

The foregoing method steps can be implemented as coded instructions in acomputer program product. In other words, the computer program productis a computer-readable medium upon which software code is recorded toperform the foregoing steps when the computer program product is loadedinto memory and executed on the microprocessor of the wirelesscommunications device.

This new technology has been described in terms of specificimplementations and configurations which are intended to be exemplaryonly. The scope of the exclusive right sought by the Applicant istherefore intended to be limited solely by the appended claims.

What is claimed is:
 1. A method of displaying a map on a wirelesscommunications device, the method comprising: obtaining map data forrendering the map to be displayed on the wireless communications device;determining a rotation angle to be applied to the map; rotating the mapby the angle of rotation by applying a single spherical correctionfactor to all vertices of the map data, the spherical correction factorbeing calculated in real-time only from a trigonometric function of therotation angle and a latitude of a center of the map; and rendering arotated and corrected map on a display of the wireless communicationsdevice.
 2. The method as claimed in claim 1 wherein the sphericalcorrection factor is equal to arctangent (tangent (the rotationangle)/cosine (the latitude)).
 3. The method as claimed in claim 1wherein the single spherical correction factor is applied when thelatitude is 40 to 50 degrees.
 4. The method as claimed in claim 1wherein obtaining the map data comprises downloading the map data over awireless link.
 5. The method as claimed in claim 1 wherein obtaining themap data comprises retrieving the map data from a local cache.
 6. Anon-transitory computer-readable storage medium comprising code recordedon the computer-readable medium that, when loaded into memory andexecuted on a processor of a wireless communications device, causes thewireless communications device to: obtain map data for rendering the mapto be displayed on the wireless communications device; determine arotation angle to be applied to the map; rotate the map by the angle ofrotation by applying a single spherical correction factor to allvertices of the map data, the spherical correction factor beingcalculated in real-time only from a trigonometric function of therotation angle and a latitude of a center of the map; and render arotated and corrected map on a display of the wireless communicationsdevice.
 7. The computer-readable medium as claimed in claim 6 whereinthe spherical correction factor is equal to arctangent (tangent (therotation angle)/cosine (the latitude)).
 8. The computer-readable mediumas claimed in claim 6 wherein obtaining the map data comprisesdownloading the map data over a wireless link.
 9. The computer-readablemedium as claimed in claim 6 wherein obtaining the map data comprisesretrieving the map data from a local cache.
 10. The computer-readablemedium as claimed in claim 6 wherein the single spherical correctionfactor is applied when the latitude is 40 to 50 degrees.
 11. A wirelesscommunications device for displaying a map, the wireless communicationsdevice comprising: an input device to cause the wireless communicationsdevice to obtain map data for rendering the map to be displayed on thedevice; a processor for determining a rotation angle to be applied tothe map and for rotating the map by the angle of rotation by applying asingle spherical correction factor to all vertices of the map data, thespherical correction factor being calculated in real-time only from atrigonometric function of the rotation angle and a latitude of a centerof the map; and a display for displaying a rotated and corrected map.12. The wireless communications device as claimed in claim 11 whereinthe spherical correction factor is equal to arctangent (tangent (therotation angle)/cosine (the latitude)).
 13. The wireless communicationsdevice as claimed in claim 11 comprising a radiofrequency transceiverfor downloading the map data over a wireless link.
 14. The wirelesscommunications device as claimed in claim 11 wherein the memory storesthe map data in a local cache.
 15. The wireless communications device asclaimed in claim 11 wherein the single spherical correction factor isapplied when the latitude is 40 to 50 degrees.